/*
 *  stdlib/setenv.c
 *
 *  This file is part of JunOS C Library.
 *  
 *  Copyright (C) 2016, Liu Xiaofeng <lxf.junos@aliyun.com>
 *  Licensed under MIT, http://opensource.org/licenses/MIT.
 */

/*
 * Copyright (c) 1987, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <errno.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>

/*
 * __findenv --
 *	Returns pointer to value associated with name, if any, else NULL.
 *	Sets offset to be the offset of the name/value combination in the
 *	environmental array, for use by setenv(3) and unsetenv(3).
 *	Explicitly removes '=' in argument name.
 *
 *	This routine *should* be a static; don't use it.
 */
static char * __findenv(const char *name, int *offset)
{
	extern char **environ;
	int len;
	const char *np;
	char **p, *c;

	if (name == NULL || environ == NULL)
		return (NULL);
	for (np = name; *np && *np != '='; ++np)
		continue;
	len = np - name;
	for (p = environ; (c = *p) != NULL; ++p)
		if (strncmp(c, name, len) == 0 && c[len] == '=') {
			*offset = p - environ;
			return (c + len + 1);
		}
	return (NULL);
}

/*
 * setenv --
 *	Set the value of the environmental variable "name" to be
 *	"value".  If rewrite is set, replace any current value.
 */
int setenv(const char *name, const char* value, int rewrite)
{
	static int alloced; /* if allocated space before */
	char *c;
	int l_value, offset;

	if (*value == '=') /* no `=' in value */
		++value;
	l_value = strlen(value);
	if ((c = __findenv(name, &offset))) { /* find if already exists */
		if (!rewrite)
			return (0);
		if (strlen(c) >= l_value) { /* old larger; copy over */
			while ((*c++ = *value++))
				;
			return (0);
		}
	} else { /* create new slot */
		int cnt;
		char **p;

		for (p = environ, cnt = 0; *p; ++p, ++cnt)
			;
		if (alloced) { /* just increase size */
			environ = (char **) realloc((char *) environ,
					(size_t) (sizeof(char *) * (cnt + 2)));
			if (!environ)
				return (-1);
		} else { /* get new space */
			alloced = 1; /* copy old entries into it */
			p = malloc((size_t) (sizeof(char *) * (cnt + 2)));
			if (!p)
				return (-1);
			memcpy(p, environ, cnt * sizeof(char *));
			environ = p;
		}
		environ[cnt + 1] = NULL;
		offset = cnt;
	}
	for (c = (char *) name; *c && *c != '='; ++c)
		; /* no `=' in name */
	if (!(environ[offset] = /* name + `=' + value */
	malloc((size_t) ((int) (c - name) + l_value + 2))))
		return (-1);
	for (c = environ[offset]; (*c = *name++) && *c != '='; ++c)
		;
	for (*c++ = '='; (*c++ = *value++);)
		;
	return (0);
}

/*
 * unsetenv(name) --
 *	Delete environmental variable "name".
 */
int unsetenv(const char *name)
{
	char **p;
	int offset;

	if (name == NULL || strlen(name) == 0 || strchr(name, '=') != 0) {
		errno = EINVAL;
		return -1;
	}

	while (__findenv(name, &offset)) /* if set multiple times */
		for (p = &environ[offset];; ++p)
			if (!(*p = *(p + 1)))
				break;
	return 0;
}
